There are applications in which it is desirable to use electron microscopy to resolve a single point-like object in a specimen. The single point-like object may be, for example, a single atom or a cluster of atoms on an amorphous substrate. Electron microscopy could theoretically be used to sequence bases of a nucleic acid, for example, such as the bases of a strand of deoxyribonucleic acid (DNA).
Scanning transmission electron microscopy (STEM), which raster scans an electron beam across a specimen, can be used to resolve single point-like objects in an image. However, STEM typically suffers from a slow scanning time, which causes poor throughput. For example, STEM may involve scanning for a time on the order of 1 μs to 10 μs per pixel of the image. This scanning time may be inadequate where sequential resolution of numerous single point-like objects is desired. STEM throughput may be inadequate, for example, for sequencing a full human genome in a practical amount of time.
Transmission electron microscopy (TEM), unlike STEM, images the specimen in parallel. But TEM imaging can be problematic when trying to resolve single point-like objects because the phase-contrast information is typically not directly interpretable for this purpose. For example, a light area in a TEM image could represent either an atom or the absence of an atom. Accordingly, although TEM may have good throughput, it does not typically yield the desired information about the specimen.
Thus, it is desirable to have electron microscopy that can reliably resolve point-like objects. It is further desirable for such electron microscopy to have substantially high throughput. Moreover, it is desirable for such electron microscopy to be provided at an affordable cost.